Various biological processes cause facial skin color changes (FSCC). FSCC are typically a result of changes in the concentration levels of hemoglobin and blood oxygenation under a user's facial skin due to a physiological response that involves changes in the user's emotional state and/or changes in the user's physical state, and/or due to normal biological processes. These changes in the concentration levels of hemoglobin and blood oxygenation can cause subtle changes in the hue and saturation components of the user's facial skin color.
There are well known methods to infer the emotional state and various physiological parameters (such as heart rate and breathing rate) of a person based on FSCC. For example, US patent application 20160098592 describes extracting emotions based on hemoglobin concentration changes (HCC) from red, green and blue (RGB) video. As another example, U.S. Pat. Nos. 8,768,438, 8,977,347, 8,855,384, 9,020,185, 8,617,081 and US patent application number 20130215244 describe extracting heart rate and related parameters from RGB video, near-IR video, and multi-spectral video streams. As still another example, the following three publications explain how FSCC (resulting from concentration changes of hemoglobin and/or oxygenation) are related to emotions: (i) Ramirez, Geovany A., et al. “Color analysis of facial skin: Detection of emotional state” in Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition Workshops, 2014; (ii) Wang, Su-Jing, et al. “Micro-expression recognition using color spaces”, in IEEE Transactions on Image Processing 24.12 (2015): 6034-6047; and (iii) Jimenez, Jorge, et al. “A practical appearance model for dynamic facial color”, in ACM Transactions on Graphics (TOG). Vol. 29. No. 6. ACM, 2010.
All the prior art methods for detecting physiological responses based on FSCC analyze video of the face taken from a camera that is remote of the user, and thus these methods typically face challenges involving face tracking and image registration. Additionally, the prior art methods do not utilize measurements of illumination interferences (such as variations in ambient light), which may, in some cases, affect the accuracy of detections of physiological responses based on FSCC. Consequently, accuracy of the prior art may be susceptible to errors that degrade the performance of detections of physiological responses based on FSCC, especially in real world, less controlled settings where the user moves and the ambient light varies.